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Friday 8 September 2017

How Does a Computer Mouse Works?

Working Principle of a Computer mouse

Every person reading this article undoubtedly have held a computer mouse in your hand.But how many of you wonder how this little device works.Here we have tried to explain 'how does a computer mouse works?'. Computer mouse is a pointing device that detects two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer on a display.Mouse is an HID (Human Interface Device) that makes your computer easy to use.Mouse can also be viewed as a cursor control device.

Types of Computer Mouse

Mainly there are two types of 'mouses'. Ball mouse(Mechanical mouse) and Optical mouse.

How does a mechanical mouse work?

mechanical ball mouse working
A ball mouse
How does a ball mouse actually work? As you move it across your desk, the ball rolls and pushes against two plastic rollers(2) mechanically connected to thin wheels (3). One of the wheels detects movements in an back-and-forth direction (say x axis),the other detects side-to-side movements (y-axis).They how they convert this movements into signals?

when you move the mouse, the ball moves the rollers that turn one or both of the wheels. If you move the mouse straight forward or backward, only the x-axis wheel turns; if you move to the right or left, only the y-axis wheel turns. And if you move the mouse at an angle, the ball turns both wheels at once.

Each wheel has slots on their edges , as it turns, the slots repeatedly break a infrared/light beam. The more the wheel turns, the more times the beam is broken. Counting the number of times the beam is broken will give how far the wheel has turned and how far you've moved the mouse. The counting,measuring and calibration are done by the microchip inside the mouse, which sends the signals down the cable to your computer. Software in your computer moves the cursor on your monitor by a corresponding amount.

How Optical mouse works?

Optical mouse working principle is entirely different from that of mechanical mouse.
An optical mouse uses a light source, typically a light-emitting diode (LED)/LASER, and a light detector, such as an array of photodiodes, to detect movement relative to a surface.

Typical optical mouse has three major parts, a light source(LED), light guiding channel(Plastic LENS) and light detector(CMOS array).
Optical mouse parts and functions
In most of the optical mouse RED LED is the light source.Plastic light guide(LENS) channels the light from the LED at an angle, down onto the desk. Light-detector chip measures light reflected back up from the desk.This CMOS light detector is a low resolution Camera.

This CMOS array takes successive images of the surface on which the mouse operates.This successive images will be processed by a DSP(Digital signal processor).Successive images will have only small differences.So, it is possible to determine in which direction mouse has moved by comparing this images.As computing power grew cheaper, it became possible to embed more powerful special-purpose image-processing chips in the mouse itself.
working of optical mouse
Illustration of successive images captured by CMOS array
Assume this is your desktop/mouse pad surface. Let 1,2 and 3 be the images captured by light detector at different instance of time t1,t2 and t3 respectively. If image 3 comes after image 1, we can easily infer that mouse moved towards right side. If image2 follows image1 ,it means mouse has moved towards left.Like this DSP determines direction of movements.

Other variants of computer mouse

Inertial and gyroscopic mice:Often called "air mice" since they do not require a surface to operate, inertial mice use a tuning fork or other accelerometer to detect rotary movement for every axis supported
3D mice:These devices generally function through ultrasound and provide at least three degrees of freedom.

logitec 3D mouse
Logitech 3D ultrasonic mouse
What we have seen here is just an abstract of working principle of mouse.Following reference links will explain the working of mouse in an elaborated way.
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